1. Field of the Invention
This invention relates to composite rings and more particularly to rings having a unidirectional substratum embedded in a polymer matrix.
2. Description of the Prior Art
Engineering achievement has long been associated with the availability of suitable materials of construction and with the development of methods of manufacture which optimize the inherent properties of the materials utilized. In recent years tremendous progress has been made in increasing the performance and durability of gas turbine engines through the use of various new metals and non-metallic materials. Further progress will depend upon the continued development of construction materials and upon the development of methods for manufacturing strong lightweight materials having increased specific stiffness and specific strength.
One group of construction materials having high specific stiffness and high specific strength are the composites which comprise a fibrous substratum embedded in a matrix. The substratum is the principle structural element of the composite and the matrix is a binder holding the substratum in a preferred orientation. Steady improvements have been made in substratum materials since glass fibers became widely used in the late 1930's and, specifically, within the aircraft industry a search for better reinforcing materials with high specific strength and high stiffness has provided numerous fibrous materials having attractive capabilities. The element boron, in particular, has been produced through recently developed techniques in a highly oriented and defect free form having the strength and stiffness properties required of fibers reinforcing compressor rotors.
The matrix in the composite structure adheres to the substratum and bonds the fibers together. Although any number of polymers including thermosplastic and thermosetting resins have been found to be suitable bonding materials, thermosetting polymides which have good thermal resistance up to temperatures of approximately 600.degree.F are particularly well suited for bonding reinforcing fibers in the compressor rotor of a gas turbine engine.
A portion of the compressor section of a typical gas turbine engine is shown in FIG. 1. The compressor includes a rotor having a plurality of blades extending radially outward therefrom. The blades are arranged in rows with each row being conventionally mounted on a compressor disk. The FIG. 1 compressor includes a composite ring embedded within the rotor beneath a central row of blades. The ring replaces a compressor disk at a substantial weight savings when compared to the more conventional disk and blade construction seen upstream and downstream of the composite ring.
The composite ring shown in FIG. 1 has been manufactured according to one prior known technique by an in situ process wherein the rotor itself serves as a mandril upon which a plurality of filaments are wound as the rotor is turned. As the filaments are wound, a polyimide resin is applied and exudes between adjacent filaments as the next layer of filaments is wound upon the mandril. The wound matrix and filament composition is subsequently cured with the aid of the compression molding tool shown in FIG. 2 which is capable of applying a radial pressure load to the composition in the disk upon actuation of an axial plunger. Additional polyimide resin is forced into the composite structure by the plunger to compress and consolidate the resin between the filaments as curing agents and solvents are evaporated from the structure. Pressures as high as 350 psi and temperatures as high as 600.degree.F are required by the described prior art method to fully consolidate and cure the matrix.
As is viewable in FIGS. 2 and 3 which are illustrative of the prior art, the filaments tend to distort during the curing process as the polyimide and fiber structure is compressed and consolidated. Deformation of the fibers from a uniformly circular pattern decreases the strength of the resulting structure and must be avoided where a high quality composite material is required. Substantial efforts are underway to produce composite rings in which the substratum of the completed article remains undistorted after the curing process.